1. Field of the Invention
The present invention relates to a mobile robot, and in particular to a mobile robot and a method for measuring a moving distance thereof capable of measuring a moving distance accurately by calculating direction and motion of a mobile robot with an image sensor.
2. Description of the Related Art
Generally, by using supersonic waves generated by plural supersonic sensors adhered to a mobile robot, the mobile robot can sense a distance or direction through reflected supersonic waves.
A robot vacuum cleaner can be a representative example of the mobile robot. The robot vacuum cleaner cleans a region to be cleaned automatically by sucking impurities such as dust, etc. from the bottom surface while moving the region automatically without being operated by a user. In more detail, the robot vacuum cleaner judges a distance to an obstacle such as furniture, office supplies and a wall, etc. in a cleaning area by using plural supersonic sensors sensing a distance and a direction, and it cleans a cleaning area by switching a direction automatically by operating a left wheel motor and a right wheel motor selectively.
FIG. 1 is a longitudinal-sectional view illustrating the conventional robot vacuum cleaner.
As depicted in FIG. 1, the conventional robot vacuum cleaner includes a fan motor 2 for generating a suction force toward a cleaner main body 1; and a filter container 4 detachably installed at the back of the fan motor 2 in order to collect dust or impurities sucked by the fan motor 2. And, a suction pipe 5 for sucking dust or impurities is installed at the back of the filter container 4, and a suction head 8 for brushing up dust or impurities on the bottom surface 6 is installed at the bottom of the suction pipe 5.
In addition, a pair of moving wheels 9 performable forward/reverse rotation is installed at the bottom of the fan motor 2, and a sub-wheel 10 is installed at the rear of the suction head 8 to support the rear end of the cleaner main body 1. And, a charge terminal unit 12 having a charge terminal 11 is installed at the rear of the cleaner main body 1, and a connection terminal 15 is formed at a power terminal unit 14 installed at an indoor wall 13 so as to be connected with the charge terminal unit 12. Accordingly, when the charge terminal 11 is connected to the connection terminal 15, a charge battery 16 disposed inside the cleaner main body 1 is charged.
In addition, a supersonic sensor 17 for transmitting/receiving supersonic waves is installed at the front center of the cleaner main body 1, and plural supersonic sensors 18 are installed at the left/right of the supersonic sensor 17 at regular intervals to sense obstacles or measure a distance to a target by transmitting supersonic waves and receiving them. And, a luminous unit 19 is installed at the lower portion of the power terminal unit 14 to induce the charge terminal unit 12 to the power terminal unit 14 by generating a light signal, and a light-receiving unit 20 is installed at the lower portion of the charge terminal unit 12 to receive the light signal from the luminous unit 19.
Reference numeral 21 is a control means for controlling various operations of the cleaner, and reference numeral 22 is an exhaust pipe.
The cleaning operation of the conventional robot vacuum cleaner will be described.
First, when a user presses an operation button, power of the charge battery 16 is applied to the fan motor 2, the fan motor 2 is operated, and a suction force is generated at the filter container 4 by the fan motor 2.
Afterward, by the suction force, dust or impurities on the bottom surface 6 is sucked into the suction head 8. The sucked dust or impurities is piled up on the filter 3 through the suction pipe 5. In addition, the control means 21 operates the moving wheels 9 by a control signal, and accordingly the cleaner main body 1 performs cleaning in a requested area while moving.
In the meantime, while performing the automatic cleaning operation, when a voltage level of the charge battery 16 is lower than a certain set level, the control means 21 stops cleaning operation. And, the control means 21 stores a present position of the cleaner in an internal memory and generates a control signal for returning the cleaner to an initial position according to a returning command preset in the memory.
Accordingly, the cleaner main body 1 is moved to the power terminal unit 14 according to the control signal of the control means 21. Afterward, when the cleaner main body 1 reaches around the power terminal unit 14, the light-receiving unit 20 installed at the lower portion of the charge terminal unit 12 receives a light signal generated by the luminous unit 19 formed at the power terminal unit 14. The control means 21 operates-controls the moving wheel 9 by the light signal received through the light-receiving unit 20, and accordingly the charge terminal unit 12 reaches the power terminal unit 14.
Next, the charge terminal 11 of the charge terminal unit 12 is contacted to the contact terminal 15 of the power terminal unit 14, and accordingly the charge battery of the cleaner main body 1 is charged by power supplied through the power terminal unit 14.
In the meantime, the robot cleaner performs cleaning operation while moving according to map information stored therein, the cleaning operation initially performed by a user's command is performed repeatedly unless layout of a cleaning area is not changed.
However, when layout of the cleaning area is changed and position of an obstacle is changed, in order to control motion, etc. of the robot vacuum cleaner, map has to be changed so as to be appropriate to the changed layout.
FIG. 2 is an exemplary view illustrating cleaning area mapping of a robot vacuum cleaner using beacon in accordance with the conventional art.
As depicted in FIG. 2, in an indoor area in which obstacles exist, the robot vacuum cleaner starts from a start point and moves by avoiding obstacles by using sensors, and accordingly a trace about a moving path is generated. Herein, the robot vacuum cleaner acquires additional information about the indoor area by receiving signals from beacons 41˜47 installed at certain portions while moving the indoor area. Accordingly, the robot vacuum cleaner performs mapping of the area on the basis of the moving path trace and the signals received from the beacons.
In the meantime, in order to perform the mapping operation, there is a need to measure a moving distance of the robot vacuum cleaner. Accordingly, the robot vacuum cleaner measures a moving distance by using an encoder for measuring rotation of a motor or an additional wheel separated from the moving wheel. In more detail, the robot vacuum cleaner calculates the number of rotations of the moving wheel by using the encoder or the wheel and multiplying a circumference of the moving wheel by the number of rotations in order to obtain a moving distance thereof.
However, when the moving wheel or the wheel is skidded, although the robot vacuum cleaner is not moved, it is calculated as the robot vacuum cleaner is moved, and accordingly accuracy of moving distance calculation may be lowered. In addition, when a mechanical type odometer is used for a robot vacuum cleaner, even the moving wheel or the wheel is not skidded, error according to wheel rotation is continually accumulated, and accordingly it is difficult to calculate a moving distance of the robot vacuum cleaner accurately. In addition, in the conventional art, by measuring a moving distance by using motion according to a mechanical structure, error may occur due to maintenance problem, impact, dust and moisture.